Figure 3

Role of ionotropic glutamate receptors in areas of the medulla containing CVPN in the tonic and baroreflex control of HR. Panel A illustrates the effects of bilateral microinjection of the NMDA antagonist MK801 (5 mM, n = 4), panel B illustrates the effects of bilateral microinjection of the AMPA antagonist CNQX (2 mM, n = 3) and panel C illustrates the effects of bilateral microinjection of CNQX following MK801 (n = 4) on resting heart rate (HR) and baroreflex bradycardia. Panel D illustrates the effects of these antagonists on resting HR. Neither MK801 nor CNQX alone altered resting HR; however, combined microinjection of these antagonists evoked a small but significant decrease in resting HR. In panel E the effect of these antagonists on baroreflex function are shown. Microinjection of MK801 evoked a modest decrease in baroreflex sensitivity (BRS) whereas microinjection of CNQX dramatically reduced BRS and abolished all baroreflex function. Combined microinjection of MK801 and CNQX reduced BRS to levels similar to that observed following microinjection of CNQX alone. * P < 0.05, ** P < 0.01.